er det muligt at have alfanumerisk sekvensgenerator i sql

Du kan oprette en funktion som denne:

create function to_base_36 (n integer) return varchar2
is
  q integer;
  r varchar2(100);
begin
  q := n;
  while q >= 36 loop
     r := chr(mod(q,36)+case when mod(q,36) < 10 then 48 else 55 end) || r;
     q := floor(q/36);
  end loop;
  r := chr(mod(q,36)+case when mod(q,36) < 10 then 48 else 55 end) || r;
  return lpad(r,4,'0');
end;

og brug det så sådan her:

select rownum, to_base_36(rownum)
from dual
connect by level < 36*36*36*36;

Eller uden at oprette en funktion:

with digits as
( select n, chr(mod(n,36)+case when mod(n,36) < 10 then 48 else 55 end) d
  from (Select rownum-1 as n from dual connect by level < 37)
)
select d1.n*36*36*36 + d2.n*36*36 + d3.n*36 + d4.n, d1.d||d2.d||d3.d||d4.d
from digits d1, digits d2, digits d3, digits d4